The present invention pertains to an internal combustion engine having an additive injector for dispensing a predetermined amount of additive into the engine lubricating oil during the periodic replacement thereof during the life of the engine, the additive preferably being silicone fluid which is known to decrease aeration of the oil. In a preferred embodiment, the injector is activated by engagement of an oil pan drain plug therewith to cause a predefined volume of silicone fluid to be transferred from a reservoir of the injector to the oil pan when the drain plug is reinserted during each oil change. In a second embodiment, the injector is incorporated in the oil filter header and releases the predetermined volume when the filter element is changed.